1. Field of the Invention
The present invention relates to an angle-resolving radar sensor, in particular for motor vehicles, including an antenna having multiple antenna elements which are each switchable to one of multiple evaluation channels and including an evaluation device for determining the angle of incidence of a received signal based on the amplitudes measured in the evaluation channels.
2. Description of the Related Art
Radar sensors are used in motor vehicles, for example, to measure distances, relative velocities, and azimuths of vehicles or other objects located ahead of one's own vehicle. Radar sensors including a group antenna having a planar design have the advantage in these applications that they only require little installation space. Individual antenna elements of the group antenna are situated at a distance from one another horizontally, so that different azimuths of the located objects result in different running times the radar signals need to travel from the object to the particular antenna element. These running time differences result in corresponding differences in the phase of the signals which are received by the antenna elements and evaluated in the associated evaluation channels. By comparing the (complex) amplitudes received in the different channels to the corresponding amplitudes in an antenna diagram, the angle of incidence of the radar signal and thus the azimuth of the located object may then be determined.
To achieve a high angular resolution, the aperture of the antenna should be as large as possible. (In the case of a planar group antenna, the aperture represents the overall extension of the group antenna in the direction of the angle measurement with regard (horizontally) to wavelength λ of the radar radiation). If, however, the distances between the adjacent antenna elements are too great, ambiguities in the angle measurement may occur, since the same phase relations between the received signals are obtained for running time differences which differ by integral multiples of wavelength λ. An unambiguous angle measurement may, for example, be obtained using a ULA (uniform linear array) structure in which the antenna elements are spaced apart at λ/2. In this case, however, the number of antenna elements and thus the number of necessary evaluation channels increases with increasing aperture, so that high hardware costs arise accordingly.